A polymer compound of the type stated at the beginning and a process of the type stated at the beginning are described in an article by R. Strümpler et al. “Smart Varistor Composites” Proc. of the 8th CIMTEC Ceramic Congress, June 1994 and in EP 875 087 B1 and WO 99/56290 A1. Doped and sintered particles of zinc oxide are provided as the filler in this polymer compound.
Typical dopants are metals, as are used in the production of metal oxide varistors and typically comprise Bi, Cr, Co, Mn and Sb. Doped ZnO powder is sintered at 800 to 1300° C. Desired electrical properties of the filler are achieved by suitable sintering temperatures and times. After the sintering, each particle has an electrical conductivity which changes as a nonlinear function on the basis of the applied electric field. Each particle therefore acts as a small varistor. The nonlinear behavior of the filler can be set within certain limits by the suitable sintering conditions. The nonlinear electrical properties of the polymer compound can therefore be set during the preparation of the compound not only by means of the filler content and the degree of dispersion but also by means of the sintering conditions of the filler.